Microporous films produced by various means have been used for breathable applications. There are a variety of thermoplastic films available on the market that exhibit breathability and liquid barrier properties. One such group of films is monolithic hydrophilic polymeric films. These films are able to transmit moisture without the additional need of fillers and stretching. The mechanism of breathability is accomplished by absorbing and desorbing moisture. One short fall of these class of films is that monolithic hygroscopic film are unsuitable for lamination to a fabric by thermo-bonding. Another shortfall is that this class of films tends to be expensive to produce and cannot be utilized for extensive end uses where cost containment is necessary. Further, to incorporate opacity characteristics into these films, high levels of pigment are needed, which further increases production costs. Primarily due to such cost concerns, laminates and garments produced from these films are not suitable for disposable applications.
Monolithic and microporous multilayer films are also known. While these films have both viral barrier capabilities as well as breathability, their manufacture is expensive and their use is not suited for disposable applications. Concurrent use of hydrophilic monolithic outer layers and a microporous core layer is described in U.S. Pat. Nos. 6,114,024 and 6,929,853 to Nicholas F. Forte (Kimberly-Clark Worldwide, Inc., Neenah, Wis.). The Forte patents, in general, describe outer layers of hydrophilic polymeric thermoplastics bonded to a core layer with microporous adhesive layers. These films cannot be used for thermo-bonding lamination, and they have monolithic layer on the skins without proper protection, which would increase the risk of pin holes. This is an expensive structure to produce as it contains the monolithic materials. U.S. Pat. No. 6,187,696 to Lim et al. (E. I. du Pont de Nemours and Company—Wilmington, Del.) discusses a moisture vapor permeable, substantially liquid impermeable composite sheet material comprising a fibrous substrate and a moisture vapor permeable thermoplastic film layer. The moisture vapor permeable film is preferably comprised of at least about 50% by weight of polymer selected from the group of block copolyether esters, block copolyether amides, polyurethanes, polyvinyl alcohol, and combinations thereof. Another version of this concept is a microporous film laminated with a monolithic film as a barrier, as described in U.S. Pat. No. 5,938,648 to LaVon et al. (Procter & Gamble Co., Cincinnati, Ohio). U.S. Pat. No. 5,938,648 also involves the use of expensive monolithic materials to act as both a barrier and a breathable layer concurrently.
EP 1 034 075 B1 to Boich (Coronor Composites GmbH) discusses a plastic film which is said to be water-tight and permeable to water vapor. The plastic film comprises at least three film layers which are said to be permanently bonded to one another. A first film layer comprises a plastic which allows the transport of water vapor on chemical pathways by absorption/desorption. The second and third film layers are provided with mineral additives, by which capillaries are implemented upon the stretching at the phase transition boundaries between plastic and mineral additives, and/or over the entire cross-section of the plastic film. The capillaries extend through the second film layer and allow the transport of water vapor on physical pathways. The layer which transports the water vapor on chemical pathways may comprise polyurethane, polyether block amide, a co-polyamide, a polyester derivative, polyester, a co-polyester, or mixtures of these materials, through which this film layer is absolutely water-tight. EP 1 034 075 B1 does not disclose the inclusion of an adhesive in the first film layer, nor that such an adhesive might be included in the multilayer film. The patent discloses that the first film layer has a thickness of 2 to 20 μm and the second film layer has a thickness of 1 to 10 μm.
The plastic film of Boich EP 1 034 075 B1 is very similar to the multilayer film described below as Comparative Example 1. That multilayer film suffered from delamination after contact with an alcohol and that in view of the similarity between Comparative Example 1 and Boich, it is submitted that the plastic film of Boich would likewise experience delamination after contact with an alcohol. Boich does not disclose a multilayer film which provides an effective barrier to alcohol based disinfectants.
U.S. Pat. No. 5,164,258 to Shida et al. discusses a multilayer structure which has a core layer of a hygroscopic barrier material and inner and outer surface layers designed to facilitate the escape of moisture which becomes absorbed in the core layer during retort sterilization. The inner and outer surface layers include a polyolefin material which is either foamed or compounded with a filler in order to cause a substantial increase in the water vapor transmission rate of the polyolefin. Adhesive layers are present between the core layer and the inner and outer layers. Each of the inner and outer layers may include one or more individual film layers, depending on the requirements of the specific packaging application.
U.S. Publication No. 20080131676 to Becke et al. (Pliant Corporation) discusses multilayer, microporous breathable barrier films and items such as laminates and garments made from such films. The films contain one or more layers of polymers without fillers in combination with at least two or more microporous breathable layers. The internal barrier layer(s) is placed in the film to impede the flow of liquids, liquid borne pathogens, and other microorganisms that may be carried by a liquid challenge. Typical materials for these barrier layers include, but are not limited to, linear low density polyethylene (LLDPE), low density polyethylene (LDPE), high density polyethylene (HDPE), ethylene/vinyl acetate (EVA), ethyl methacrylate (EMA), polypropylene (PP), copolymers of PP, copolymers of polyethylene (PE) and PP, derivatives thereof, and combinations thereof. A variety of additives may be added to the barrier layers to provide additional properties such as antimicrobial effects, odor control, and static decay.
Other common breathable films are microporous films. These films exhibit exceptional breathability, but do not provide a barrier to microorganisms and some liquids depending on the pore size and exposure conditions. Multilayer microporous films are also known in the art. U.S. Pat. No. 5,955,187 to McCormack (Kimberly-Clark Worldwide, Inc., Neenah, Wis.) discusses a self-regulating breathable microporous film layer that includes a voided polymer matrix and a plurality of fine water-swellable filler particles disposed within the voids. Multilayer microporous films having a microporous filled core layer and skin (outside) layers are discussed in U.S. Pat. No. 6,075,179, to McCormack et al. (Kimberly-Clark Worldwide, Inc., Neenah, Wis.) and U.S. Pat. No. 6,682,803 (Kimberly-Clark Worldwide, Inc., Neenah, Wis.). This skin/core concept does not impede the transmission of viruses or other challenge materials as they are able to pass through the cracks in the resultant film's outer skin layer
Other methods of making microporous films involve the phase separation of various polymers, leaving voids and areas of low crystallinity as pathways for breathability. These pathway structures do not impede the transmission of viruses or other challenge materials as they are able to pass through the voids and amorphous areas in the film. These methods are described in U.S. Pat. No. 4,539,256 to Shipman, U.S. Pat. No. 5,260,360 to Mrozinski, U.S. Pat. No. 5,690,949 to Weimer, et al., U.S. Pat. No. 5,738,111 to Weimer, et al. (all five assigned to Minnesota Mining and Manufacturing Co., St. Paul, Minn.), and U.S. Pat. No. 5,938,874 to Palomo, et al. (Allegiance Corporation, McGaw Park, Ill.), among others.
U.S. Pat. No. 5,935,370 to Weimer (3M) discusses a microporous membrane material comprising (1) a thermoplastic polymer or polytetrafluoroethylene and (2) a water- and oil-repellent fluorochemical compound which provides said membrane with oleophobic, hydrophobic and viral barrier properties.